Which pharmaceutical is known to dilate the pupil for 3-6 hours?

Cyclopentolate at a concentration of 1% is recognized for its effectiveness in dilating the pupil, a process known as mydriasis. This drug is frequently used in ophthalmic examinations to allow for a better view of the retina and other internal structures of the eye. The duration of its pupil-dilating effect typically lasts between 3 to 6 hours, making it suitable for short to medium-duration procedures or examinations.

The other options may have different effects or durations of action. For example, while atropine is a potent mydriatic agent, its effects can last significantly longer than 6 hours, sometimes up to several days, which is often not desired for routine examinations. Phenylephrine, primarily a sympathomimetic agent, can induce pupil dilation but its duration of effect may not align perfectly with the specified 3-6 hour window in many cases. Tropicamide, although it does induce dilation, generally has a shorter duration than cyclopentolate, often lasting only 1 to 4 hours. This makes cyclopentolate the most appropriate choice for this particular question.